Split-nut blade locking assembly

ABSTRACT

A split-nut blade locking assembly, for maintaining the circumferential integrity of blades peripherally disposed within a groove around a rotor element includes a split-nut within which a set screw may be threadably engaged for spreading apart the halves of the split-nut and maintaining the halves in engagement with the side walls of the groove.

United States Patent Anderson 1 51March 20, 1973 541 SPLIT-NUT BLADE LOCKING 3,216,700 11/1965 Bostock ..4l6/216 ASSEMBLY Y FOREIGN PATENTS OR APPLICATIONS [75] Inventor: Bernard Joseph Anderson, Danvers,

Mass. 840.797 5 1970 Canada ..41e/215 639,320 6/1950 Great Britain ..4l6/2I5 [73] Assignee: eneral Electric Company, Lynn. 659,592 10 1951 Great Britain.... ...4l6/215 Mass; 703,173 1/1954 Great Britain ..416/215 [22] May 1971 Primary ExaminerEverette A. Powell, Jr. [21] Appl. No.: 146,732 Attorney-Derek P. Lawrence et al.

521 0.5. CI ..416/2l5, 416/220 [57] ABSTRACT l l A split-nut blade locking assembly, for maintaining the 0 Search l l 5, 2 l 6, circumferential integrity of blades peripherally disposed within a groove around a rotor element in- References Cited cludes a split-nut within which a set screw may be UNITED STATES PATENTS threadably engaged for s areading apart the halves of the split-nut and maintaining the halves in engagement 1,687,891 10/1928 Ray 416/216 with the side walls of the groove. 2,315,631 4/1943 Lloyd et alm. .....416/2I6 2,918,255 12/1959 McGinnis ..416/216 7 Claims, 5 Drawing Figures 3,088,708 5/1963 Feinberg ..4l6/2I5 PATENTFDHARZOISB v 3, 1,5 5

sum 1 HF 2 EM Km PATENTEUmmeo1217a sum 2 or 2" Y. INVENTOR.

Eff/V480 J. Ava/0521a SPLIT-NUT BLADE LOCKING ASSEMBLY The invention herein described was made in the course of or under a contract or subcontract thereunder, (or grant) with the Department of the Navy.

BACKGROUND OF THE INVENTION In general, this invention relates to a split-nut blade locking assembly and more particularly to a split-nut blade locking assembly for securing a plurality of circumferentially spaced blades disposed about the periphery ofa rotor disc.

In the axial flow compressor art it is well known to dispose a plurality of circumferentially spaced blades about the outer periphery of a rotor disc element. Each blade so disposed includes a vane section extending outward from the periphery of the rotor disc and a root portion extending in a substantially inward radial direction from the periphery of the rotor disc. It is also well known in the art to radially and axially retain the blades in the rotor by means of a dovetail groove around the outer periphery thereof. The blade root portions are thickened at the inner radial end to provide outwardly extending shoulders which abut the inwardly directed faces of the dovetail groove. Assembly of the blade roots into the dovetail groove is ordinarily accomplished by inserting a blade root through a narrow, square-cornered entrance slot, cut into the dovetail groove at one or more discreet points along the circumference of the spool and then sliding the blades in the dovetail groove into their respective positions. Means must be provided for locking the blades in circumferential position along the periphery of the rotor disc. The locking means must be capable of withstanding the circumferential component of the aerodynamic load developed during compressor operation. At the same time, the locking device must be capable of permitting assembly and disassembly of the blade members to the spool with relative ease.

Difficulties have been encountered in providing a satisfactory means for locking the blades in circumferential position along the periphery of the rotor disc. Past means have often taken the form of set screw arrangements or spring load devices which have reliability limitations, or are difficult to contend with during assembly and disassembly of the rotor. These devices are of very small physical size and are, therefore, often limited in strength. Other shortcomings of prior art devices relate to the necessity that the entire circumferential row of blades be rotated as a unit, one-half a blade pitch about the periphery of the rotor disc at assembly and disassembly. This often results in damaged blades due to the tendency of blades to seize after prolonged service. Also, conventional locking means are often visually concealed after all blades are inserted thereby prohibiting subsequent visual inspection.

Further, conventional narrow, square-cornered entrance slots inherently tend to concentrate stresses at the corners which reduce the overall fatigue life of the part.

It is therefore an object of this invention to provide a blade locking assembly which permits ready assembly and disassembly of the blades of a rotor disc element, yet provides positive locking of the blades in position during rotor rotation.

It is another object of the invention to provide a blade locking assembly which includes a set screw of substantially larger size than heretofore possible, thereby overcoming the inherent strength limitations previously attributable to blade locking assemblies having set screws.

It is a further object of this invention to provide a blade locking assembly wherein the blades may be assembled and disassembled from the rotor disc without having to rotate the entire circumferential row of blades as a unit, one-half a blade pitch.

It is another object of this invention to provide an inexpensive entrance slot which does not inherently concentrate stresses at square corners.

It is a further object of this invention to provide a locking assembly which remains externally visible after all blades have been inserted so that positive locking may be visually assured.

SUMMARY OF THE INVENTION The split-nut blade locking assembly of this invention includes a wrenching set screw and a split-nut positioned within a dovetail groove. The wrenching set screw has an external thread around the body thereof. The split-nut includes a split-collar wherein the inside surface of the split-collar includes a screw thread for threadably engaging the set screw. The two arcuate segments of the split-collar further include flange members having sides which extend outwardly into shoulders adapted for engagement with the inwardly directed faces of a dovetail groove. Threadably engaging the set screw within the split-nut acts to spread apart the halves of the split-nut and maintain the shoulders in engagement with the faces of the dovetail groove. 4

DESCRIPTION OF THE DRAWINGS While the specification concludes with claims distinctly claiming and particularly pointing out the invention described herein, it is believed that the invention will be more readily understood by reference to the discussion below and the accompanying drawings in which:

FIG. 1 is a perspective view showing the locking assembly of this invention as assembled within a rotor disc.

FIG. 2 is an exploded perspective view showing the locking assembly of FIG. 1 in combination with a rotor disc.

FIG. 3 is a perspective view showing a rotor blade positioned within an entrance slot in the periphery of the rotor.

FIG. 4 is a cross-sectional view of FIG. 1 taken along the line 4-4.

FIG. 5 is an exploded perspective view showing an alternate embodiment for the locking assembly of FIGS. 1 and 2 in combination with a rotor disc.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a portion of a rotor assembly 10 of the type commonly included in an axial flow compressor which may form an integral part of a gas turbine engine. The rotor assembly 10 is shown as including a rotor disc 11 having axially spaced apart, opposed faces 12 and 14, both of which are substantially normal to the axis of rotor rotation.

The rotor disc 11 includes a plurality of circumferentially spaced apart blades 22 and 24 disposed about its periphery. The blades 24 and end locking blades specially adapted to accommodate the split nut blade locking assembly of this invention shown generally at 37 and which will hereinafter be described in full detail. Each of the blades 22, 24 includes an airfoil vane section 26 through which gas flow may be directed for compression in a manner well known to the art. The blades 22, 24 also include platforms 28, 30

respectively from which dovetail root portions 32 extend in substantially inward radial directions. The platforms generally overhang the root portions.

The blades 22, 24 are radially and axially retained by means of a circumferential dovetail groove 16 extending around the outer periphery of the rotor disc 11. The dovetail groove 16 includes a pair of side walls 18 which are undercut to provide inwardly directed abutment faces 20. Each dovetail root 32 is thickened at the inner radial end to provide outwardly extending shoulders 34 which abut the inwardly directed faces of the dovetail groove, thereby radially retaining the blades under centrifugal loading.

Referring now to FIG. 2, the circumferential dovetail groove 16 includes a circular entrance slot 36 therein, to accommodate insertion of the individual blade root portions 32 into the dovetail groove 16. Each blade root portion 32 is individually inserted through the circular entrance slot 36 for engagement with the opposing surfaces of the dovetail groove 16. After insertion each blade 22 is circumferentially slid around the dovetail groove 16 into platform abutting relation with an adjacent blade until all the inserted blades circumferentially fill the dovetail groove. The last two blades to be inserted are the end locking blades 24.

Referring now to FIG. 3 in conjunction with FIG. 2 there is shown the last inserted locking blade 24 nested within the circular entrance slot 36 and aligned for sliding engagement with the dovetail groove 16. As may be readily observed, the circular entrance slot 36 is of sufficiently large radius to accommodate insertion of the substantially rectangular cross-sectional root portion 32 of the end locking blade 24. The root portions ofthe conventional blades 22 are identical to the root portions of the end locking blades 24, and are inserted into the entrance slot for engagement with the dovetail groove in like manner. All of the root portions 32 include opposing transverse faces 35, 35' extending across the dovetail groove. The opposing transverse faces 35, 35 generally lie in the plane of intersection of a rotor radius with the central axis of rotation, and are normal to the side walls 18 of the circumferential dovetail groove 16. The opposing transverse faces 35, 35, however, are not inherently limited to any particular plane and may be skewed in relation to the side walls 18 of the dovetail groove 16.

In order to minimize the arc distance between the end locking blade vanes after insertion of the split-nut locking assembly, the locking blade platforms are indented along the edges 56, 56' so as to align the edges of the blade platforms with the respective transverse faces 35, of the root portions. Even though the locking blade platforms 30 are indented along the edges 56, 56' an additional space equal to as much as half a blade pitch may still remain between the end locking blade vanes after insertion of the split-nut locking assembly. This spacing, however, has been found not to adversely affect engine performance. After the last locking blade 24 is nested within the circular entrance slot 36 as shown in FIG. 3, it is then slid into engagement with the dovetail groove 16 as shown in FIG. 2.

The split-nut locking assembly is also shown in FIG. 2 at 37 as including a split-nut 38 and an internal wrenching set screw 46. The use of a split-nut together with a circular entrance slot makes possible the inclusion of a larger set screw than heretofore possible with the smaller conventional square cornered locking slots. The split-nut 38 includes a split collar 39 having two arcuate segments 40, 40'. Outside surfaces 41, 41' of arcuate segments 40, 40' are proportioned for abutting engagement with the inside surfaces of the circular entrance slot 36. Arcuate segments 40, 40' of the splitcollar 39 respectively include flange members 43, 43. The flange members 43, 43' respectively have outwardly extending shoulders 44, 44' for engagement with the inwardly directed abutment faces 20 of the sidewalls 18 of the dovetail grooves 16. The ends of the flange members 43, 43' cooperate together to form split-transverse abutment faces 54, 54'.

The split-collar 39 includes an internal screw thread which is threadably engaged to the external screw thread of the wrenching set screw 46. The wrenching set screw 46 also includes a hexagonal insert 52 in the top surface thereof, adapted for receiving an Allen wrench or the like.

In order to lock the blades into fixed position on the circumference of the rotor disc 11 after all the blades have been inserted into the groove in the previously described manner, the split-nut 38 is inserted into the area of the circular entrance slot 36 and dovetail groove 16 in a manner so that the outer surfaces 41, 41' of the arcuate segments of the split-collar 39 abut the interior surfaces of the circular entrance slot and each outwardly extending shoulder 44, 44' engages a corresponding inwardly directed abutment face 20 of the dovetail groove 16. The split-transverse abutment faces 35, 35' engage the respective transverse faces 35, 35' of the root portions 32 of the locking blades 24. The split halves of the nut 38 are spread apart and maintained in abutting and engaging relation with the dovetail groove 16 by insertion of the wrenching set screw 46 which threadably engages the split-nut 38. The wrenching set screw 46 may be safety locked into position by peening over the top thread on the split-nut 38. Therefore, the split-nut 38 is preferably made from a softer and more ductile material than the wrenching set screw 46 to facilitate peening and to make it possible to disassemble by threading the set screw out, so as to reform the peened thread.

As is readily obvious from reference back to FIG. I, circumferential sliding of the split-nut blade retention assembly 37 around the peripheral dovetail groove of the rotor disc 11 is inhibited by the abutting relation of the outside surfaces 41, 41' of the split-collar with the inside surface of the circular entrance slot 36. Circumferential sliding of the blades 22, 24 around the peripheral dovetail groove of the rotor disc 11 is positively inhibited by the abutting relation of the splittransverse abutment faces 54, 54' with the respective transverse faces 35, 35' of the root portions 32 of the locking blades 24. Radial withdrawal of the split-nut blade retention assembly is also prohibited by engagement of the outwardly extending shoulders 44,44 with the inwardly directed abutment faces of the dovetail groove 16.

The split-nut blade retention assembly may be withdrawn by inserting an Allen wrench or the like into the hexagonal insert 52 in the top surface of the set screw 46 and threadably disengaging the set screw from the split-nut. After the set screw is withdrawn, the splitnut may be removed, whereupon each blade may be circumferentially slid into the area of the circular entrance slot 36 and withdrawn in a generally radial direction. Of particular advantage over known blade locking assemblies is the ability to insert individual blades and to slide the individual blades around the circumference of the rotor disc 11. Heretofore, in order to insert or withdraw blades from a rotor disc, it was required that the entire stage of blades be rotated as a unit one-half blade pitch, which on occasion would pose considerable difficulty due to the tendency of the blades to seize after long periods of service.

It is preferred that the wrenching set screw 46 be formed with double lead threads around the body thereof. The double lead threads are shown in FIG. 2 as including a primary lead thread 48 and a secondary lead thread 50, wherein both ends of the primary and secondary threads are 180 apart from each other on the circumference of the screw. The split-nut 38 also would include internal double lead threads for threadably receiving the set screw 46. The double lead threads are preferred because they permit the halves of the split-nut 39 to be interchanged thereby eliminating the need to match the halves of each split-nut. Also, although the insert 52 on the top of the set screw 46 has been described as hexagonal in shape, it need not be so limited and may include any shape to which a tool may be keyed so as to provide increased torque so as to either tighten the set screw or remove the set screw once it has been tightened.

Referring now to FIG. 5 where like numerals designate previously described elements, there is shown an alternate embodiment for the split-nut blade retention assembly of FIGS. 1 through 4. The split-nut retention assembly is shown generally as including a split-nut 60 which consists, of a split-collar 61 having two arcuate segments 62, 62'. Again the outside surfaces of the arcuate segments are proportioned for abutting engagement with the inside surfaces of the circular entrance slot 36. Arcuate segments 62, 62' of the split-collar 61 include respectively flange members 63, 63. The flange members 63, 63' respectively include shoulders 64, 64 extending outwardly in opposing directions for engagement with the inwardly directed abutment faces 20 of the sidewalls 18 of the dovetail slot 36. The halves of the split nut are then spread apart so that the outwardly extending shoulders 64, 64. engage the inwardly directed abutment faces 20 of the dovetail groove and the transverse faces 66, 66' abut respectively opposing transverse faces 35, 35' of the blade roots. The split halves of the nut are maintained in spread apart relation by insertion of the wrenching set screw 46 which threadably engages the split-nut 60. Withdrawal of the locking assembly may be accomplished by reversing the previously described process.

While preferred embodiments of the present invention have been depicted and described, it will be appreciated by those skilled in the art that many modifications, substitutions and changes may be made thereto without departing from the inventions fundamental theme.

Having thus described one embodiment of the invention, what is desired to be secured by letters patent is as follows:

1. A split-nut locking assembly for attachment to a groove comprising:

a wrenching set screw having an external thread around the body thereof;

and a split-nut including a split-collar having two arcuate segments, the inside surfaces of which are threaded for threadably engaging the set screw, and wherein the arcuate segments of the split-collar integrally connect to flange members having sides which extend outwardly into shoulders adapted for engagement with the sidewalls of the groove when the set screw is threadably engaged within the split-nut so as to spread apart the halves of the split-nut.

2. A split-nut locking assembly for locking a plurality of circumferentially spaced blades disposed about the outer periphery of a grooved rotor disc comprising:

a wrenching set screw having an external thread around the body thereof;

and a split-nut including a split-collar having two arcuate segments, the inside surfaces of which are threaded for threadably engaging the set screw, and wherein the arcuate segments of the split-cob lar integrally connect to flange members having sides which extend outwardly into shoulders adapted for engagement with the sidewalls of the groove when the set screw is threadably engaged within the split-nut so as to spread apart the halves of the split-nut.

3. The assembly of claim 2 wherein:

the side walls of the groove are undercut to provide inwardly directed abutment faces for engaging the outwardly extending shoulders of the split-nut and including at least one circular entrance slot through the inwardly directed abutment faces of the groove to accommodate insertion of the flange members ofthe split-nut within the groove, and

each blade has a vane section extending outward from the periphery of the rotor disc and a root portion extending in a substantially inward radial direction from the periphery of the rotor disc, with each root thickened at the inner radial end to provide outwardly extending shoulders which abut the inwardly directed faces of the groove so as to radially and axially retain the blades with circumferential retention of the blades along the peripheral groove maintained by the split-nut the outwardly extending shoulders of which also engage the inwardly directed faces of the groove upon threadable engagement of the set screw within the split-nut.

4. The assembly of claim 3 wherein each blade includes an overhanging platform disposed between the vane and root portion such that the blades may be circumferentially arranged around the peripheral groove in platform abutting relation and wherein the platforms of the two blades adjacent the split-nut are indented to accommodate insertion of the split-nut while maintaining a minimum arc distance between the blades adjacent to the split-nut.

5. The assembly of claim 3 wherein the set screw and split-nut include double lead threads to allow interchange between the halves of the split-nut.

6. The assembly of claim 3 wherein:

each blade root portion includes a pair of opposing transverse faces extending across the dovetail groove, and wherein each flange member of an arcuate segment of the split-collar includes an outwardly extending shoulder for engagement with a face of the groove and the respective ends of both flanges cooperate together to form split transverse faces such that circumferential sliding of the splitnut and set screw around the peripheral groove of the rotor disc is inhibited by abutment between the outside surface of the split collar with the inside surface of the circular entrance slot, circumferential sliding of the blades around a the peripheral groove of the rotor disc is inhibited by abutment between the split transverse faces of the split-nut and the respective transverse faces of the blade root portions and outward radial withdrawal of the split-nut is prohibited by engagement of the outwardly extending shoulders with the inwardly directed abutment faces of the peripheral groove. 7. The assembly of claim 3 wherein each blade root portion includes a pair of opposing transverse faces extending across the dovetail groove, and wherein each flange member of an arcuate segment of the split-collar includes a pair of oppositely extending shoulders for engagement with the opposing faces of the groove and the end of each flange terminates in a transverse face, wherein circumferential sliding of the split-nut and set screw around the peripheral groove of the rotor disc is inhibited by abutment between the outside surface of the split-collar with the inside surface of the circular entrance slot, circumferential sliding of the blades around the peripheral groove of the rotor disc is inhibited by abutment between the transverse faces of the split-nut and the respective transverse faces of the blade root portions and outward radial withdrawal of the split-nut is prohibited by engagement of the outwardly extending shoulders with the inwardly directed abutment faces of the peripheral groove. 

1. A split-nut locking assembly for attachment to a groove comprising: a wrenching set screw having an external thread around the body thereof; and a split-nut including a split-collar having two arcuate segments, the inside surfaces of which are threaded for threadably engaging the set screw, and wherein the arcuate segments of the split-collar integrally connect to flange members having sides which extend outwardly into shoulders adapted for engagement with the sidewalls of the groove when the set screw is threadably engaged within the split-nut so as to spread apart the halves of the split-nut.
 2. A split-nut locking assembly for locking a plurality of circumferentially spaced blades disposed about the outer periphery of a grooved rotor disc comprising: a wrenching set screw having an external thread around the body thereof; and a split-nut including a split-collar having two arcuate segments, the inside surfaces of which are threaded for threadably engaging the set screw, and wherein the arcuate segments of the split-collar integrally connect to flange members having sides which extend outwardly into shoulders adapted for engagement with the sidewalls of the groove when the set screw is threadably engaged within the split-nut so as to spread apart the halves of the split-nut.
 3. The assembly of claim 2 wherein: the side walls of the groove are undercut to provide inwardly directed abutment faces for engaging the outwardly extending shoulders of the split-nut and including at least one circular entrance slot through the inwardly directed abutment faces of the groove to accommodate insertion of the flange members of the split-nut within the groove, and each blade has a vane section extending outward from the periphery of the rotor disc and a root portion extending in a substantially inward radial direction from the periphery of the rotor disc, with each root thickened at the inner radial end to provide outwardly extending shoulders which abut the inwardly directed faces of the groove so as to radially and axially retain the blades with circumferential retention of the blades along the peripheral groove maintained by the split-nut, the outwardly extending shoulders of which also engage the inwardly directed faces of the groove upon threadable engagement of the set screw within the split-nut.
 4. The assembly of claim 3 wherein each blade includes an overhanging platform disposed between the vane and root portion such that the blades may be circumferentially arranged around the peripheral groove in platform abutting relation and wherein the platforms of the two blades adjacent the split-nut are indented to accommodate insertion of the split-nut while maintaining a minimum arc distance between the blades adjacent to the split-nut.
 5. The assembly of claim 3 wherein the set screw and split-nut include double lead threads to allow interchange between the halves of the split-nut.
 6. The assembly of claim 3 wherein: each blade root portion includes a pair of opposing transverse faces extending across the dovetail groove, and wherein each flange member of an arcuate segment of the split-collar includes an outwardly extending shoulder for engagement with a face of the groove and the respective ends of both flanges cooperate together to form split transverse faces such that circumferential sliding of the split-nut and set screw around the peripheral groove of the rotor disc is inhibited by abutment between the outside surface of the split collar with the inside surface of the circular entrance slot, circumferential sliding of the blades around the peripheral groove of the rotor disc is inhibited by abutment between the split transverse faces of the split-nut and the respective transverse faces of the blade root portions and outward radial withdrawal of the split-nut is prohibited by engagement of the outwardly extending shoulders with the inwardly directed abutment faces of the peripheral groove.
 7. The assembly of claim 3 wherein each blade root portion includes a pair of opposing transverse faces extending across the dovetail groove, and wherein each flange member of an arcuate segment of the split-collar includes a pair of oppositely extending shoulders for engagement with the opposing faces of the groove and the end of each flange terminates in a transverse face, wherein circumferential sliding of the split-nut and set screw around the peripheral groove of the rotor disc is inhibited by abutment between the outside surface of the split-collar with the inside surface of the circular entrance slot, circumferential sliding of the blades around the peripheral groove of the rotor disc is inhibited by abutment between the transverse faces of the split-nut and the respective transverse faces of the blade root portions and outward radial withdrawal of the split-nut is prohibited by engagement of the outwardly extending shoulders with the inwardly directed abutment faces of the peripheral groove. 